Photosynthetic contribution of UV-A to carbon fixation by macroalgae

Previous studies showed that energy of ultraviolet light A (UV-A) (315-400 nm) could be used for photosynthesis by some macroalgae; however, little has been documented on the extent of such photosynthetic contribution among different macroalgal taxa. We selected 11 macroalgal species, representing red, brown and green phyla, and investigated their ability to utilize UV-A for photosynthesis. Our results showed that, in the absence of photosynthetically active radiation (PAR), UV-A alone triggered photosynthetic carbon fixation rates in all the selected species. The gross photosynthetic rates of the tested macroalgae when exposed to UV-A ranged from 6.5 +/- 0.3 to 52.3 +/- 1.8 mu mol C g (fresh weight)(-1) h(-1), with the highest rate found in the green alga Ulva lactuca Linnaeus. The ratio of gross photosynthesis driven by UV-A alone to that by saturating PAR varied from 14% to 22%. The present work demonstrated that macroalgae are capable of utilizing UV-A irradiance to drive photosynthetic carbon fixation, and this was consistent for all the species tested across green, red and brown algae.